1. Field of the Invention
The present invention relates to a plasma processing method and apparatus. Particularly, the present invention relates to a plasma processing method employed typically in film deposition, etching treatment, and the like. The plasma processing method employed in film deposition specifically includes a plasma CVD film-forming method for forming a semiconductor film or a insulator film usable in the production of semiconductor devices such as electrophotographic light receiving members (or electrophotographic photosensitive members), photovoltaic elements (including solar cells), image input line sensors, image pickup devices, and the like. The present invention also relates to a plasma processing apparatus suitable for practicing said plasma processing method.
2. Related Background Art
For the photoconductive material to constitute a light receiving layer in a light receiving member which is used in the field of electrophotographic image formation, it is required to be highly sensitive, to have a high SN ratio [photocurrent (Ip)/dark current (Id)], to have an absorption spectrum compatible for the spectrum characteristics of an electromagnetic wave to be irradiated, to have a quick photoresponsibility and to have a desired dark resistance. It is also required to be not harmful to living things as well as human upon use. Especially in the case where the light receiving member is used as an electrophotographic light receiving member which is installed in an electrophotographic apparatus as a business machine in offices, causing no pollution is indeed important.
From these standpoints, there have been proposed a variety of electrophotographic light receiving members comprising an amorphous silicon (a-Si) material compensated by, for instance, hydrogen atoms (H) or/and halogen atoms (X) (such as fluorine atoms, chlorine atoms, or the like. Some of these electrophotographic light receiving members already have been put to practical use. [The electrophotographic light receiving member comprising such a-Si material will be hereinafter referred to as "a-Si electrophotographic light receiving member".]
Such a-Si material substantially satisfies all the above described requirements and excels in durability. Therefore, the a-Si material is an excellent constituent material of the electrophotographic light receiving member.
However, in comparison with a so-called OPC electrophotographic light receiving member comprising an organic semiconductor material (an organic photoconductive (OPC) material in other words) which has been widely spread in recent years, the a-Si photoelectric light receiving member is relatively costlier. In view of this, there is an increased demand for developing a highly productive film-forming method and apparatus which enables one to stably mass-produce high quality a-Si electrophotographic light receiving members.
Now, for the formation of an amorphous silicon (a-Si) deposited film, there have been proposed various film-forming methods. Of these film-forming methods, so-called plasma CVD film-forming methods in which a given raw material gas is decomposed by means of an electric field of D.C., RF, VHF (very high frequency) or MW (microwave) to form a deposited film on a substrate have been popularized, for the reason that according to these plasma CVD film-forming methods, a desired large area deposited film can be relatively easily formed.
In addition, in recent years, there have been proposed some plasma CVD apparatus in which such plasma CVD film-forming method is practiced, which are aimed at improving the productivity of forming a deposited film. For instance, U.S. Pat. No. 4,972,799 discloses a plasma CVD film-forming apparatus by a microwave plasma CVD process (that is, a microwave plasma CVD film-forming apparatus) which is characterized by having a holding member, which is capable of holding a microwave introducing window and a plurality of substrates concentrically arranged around the microwave introducing window and which is capable of sealing a deposition chamber in a air-tight state upon film formation, and a means for transporting said holding member under vacuum condition. In this document, there is described as follows. That is, the microwave plasma CVD film-forming apparatus is provided with a plurality of deposition chambers and a movable vacuum vessel which serves to assemble a microwave introducing means including said microwave introducing window and said substrates onto said holding member. The assemble comprising the microwave introducing means and the substrates fixed onto the holding member is transported into one of the deposition chambers under vacuum condition through the movable vacuum vessel where the formation of a deposited film on the substrates is conducted, then the assemble after the film formation is taken out from the deposition chamber through the movable vacuum vessel. In the case where further film formation is desired, the assemble is transported into other deposition chamber in the same manner as described above. In this way, there can be mass-produced deposited films.
According to this microwave plasma CVD film-forming apparatus, since the film formation in each deposition chamber can be continuously conducted without breaking the vacuum and while preventing contamination of dust, an improvement in the productivity and quantity production of deposited film can be attained to a certain extent and the mass-production of deposited films having an improved quality can be attained.
However, in this microwave plasma CVD film-forming apparatus, there is a limit to a certain extent for the film formation cycle, because the speed for the holding member to be transported into a given deposition chamber has a limitation because it unavoidably takes a certain period of time upon precisely positioning the holding member and the like as required. In addition, there is a disadvantage such that in the case of heating the substrates on the holding member prior to the film formation or in the case where after the holding member is transported into a given deposition chamber, the substrates thereon are heated and subjected to the film formation, the occupation time of the deposition chamber is prolonged and this situation is inefficient. In order to improve this advantage, it is considered to be effective that a heating vacuum vessel is provided, and after previously heating the substrates on the holding member in this heating vacuum vessel, the holding member is transported into the deposition chamber. However, this manner is not always effective for the reason that since the speed for the holding member to be transported into the deposition chamber has such limitation as above described, during the transportation of the holding member into the deposition chamber, the temperature of the substrates on the holding members is liable to change, resulting in affecting the properties of deposited films formed on the substrates in the deposition chamber.
Separately, in recent years, electrophotographic apparatus have been improved to have a high performance and they have been diversified. Along with this, for electrophotographic light receiving members used in such electrophotographic apparatus, they are necessary to be more improved with respect to their quality so that they can stably and continuously reproduce a high quality image. In addition, they are also necessary to be improved to have variations so as to comply with use purposes.
Further, in recent years, there has been a tendency that the space occupied by business machines including an electrophotographic apparatus in an office is diminished as smaller as possible in order to save the office space for other purposes. In this connection, electrophotographic apparatus have been miniaturized. For electrophotographic light receiving members used in such electrophotographic apparatus, it is indispensably necessary for them to conform such electrophotographic apparatus. In this respect, it is necessary to provide an appropriate electrophotographic light receiving member having a more improved performance at a reasonable cost which can satisfy such demand.